1. Field of Invention
The present invention relates to a liquid ejecting apparatus in which a liquid ejecting head ejecting a liquid such as ink performs cleaning and a method of cleaning the liquid ejecting head of the liquid ejecting apparatus.
2. Description of Related Art
As such a liquid ejecting apparatus, for example, an ink jet printer (hereinafter, referred to as “printer”) is described in JP-A-11-342634. The printer described in JP-A-11-342634 is provided with a plurality of head units (printing head) as a liquid ejecting head that ejects ink as a liquid onto a target such as a printing sheet, and ink tanks and sub-tanks that accommodate ink supplied into the head units. At the time of a purge operation of removing bubbles and solids in the ink from the head unit, the ink tank is pressurized by driving an air pump, the ink is supplied from the ink tank to each head unit through a circulation going path, a part of ink which is not discharged from each head unit is stored in the sub-tank through a circulation returning path. The ink which is temporarily stored in the sub-tank after the purge operation is ended is returned to the ink tank and is reused.
The ink circulation printer described in JP-A-11-342634 is configured so that at the time of cleaning, a part of the ink which is not discharged from each head unit flows back to the sub-tank through the circulation return path, bubbles and the like included in the ink in the printing head are removed by the circulating ink flow, and it can be expected that they are recovered in the sub-tank.
In this case, the cleaning effect of removing the bubbles can be improved by raising the flow velocity of the ink flowing in the printing head. In order to raise the ink flow velocity, it is necessary to improve the capability of a pressurization pump. Accordingly, there is a problem that it is difficult to obtain a good cleaning effect in proportion to the capability of the pump. In the printer described in JP-A-11-342634, since the ink is also discharged from nozzles, and a flow rate of the ink flowing toward the circulation return path in the printing head is decreased as much as the amount of ink used for discharge from the nozzles as compared with the flow rate of the ink supplied to the printing head, thus there is a problem that effective cleaning cannot be expected.
Since nozzle cleaning of compulsorily discharging the ink from the nozzles of the printing head is performed by circulating the ink, it is impossible to sufficiently raise the pressure of the ink in the printing head by flowing back the ink, and it is difficult to strongly discharge the ink from the nozzles.
Particularly, in the case of using ink with a relatively high viscosity as compared with aqueous ink, such as UV (Ultra Violet) ink (ultraviolet ray curable ink) cured by irradiation of ultra violet rays, it is necessary to make an ink flux strong to that extent to perform cleaning, but such a method is not disclosed. For this reason, in order to improve the cleaning effect, it is necessary to provide a large apparatus exclusively for cleaning.